Blender Git Loki

Make GPU buffers allocation/freeing safe for threading

Code in GPU_buffers_free was already trying to be safe
for threading, by skipping OGL calls there, but in fact
it was still buggy.

Namely, freeing was doing buffers shift in a cycle, and
if two threads will call this function shifting will go
crazy.

Now made it so GPU_buffers_alloc and GPU_buffers_free
are using mutex lock, so they're completely safe for
threading. Same goes to gpu_buffer_setup function.

It required minor functions reshuffle, so there're no
locks happening from locked thread, but it's all very
straightforward change.